(a) Field of the Invention
The present invention relates to a display device.
(b) Description of the Related Art
A liquid crystal display (LCD) among display devices includes an upper panel provided with a common electrode and an array of color filters and a lower panel provided with a plurality of thin film transistors (TFT) and a plurality of pixel electrodes. Alignment layers are coated on the upper panel and the lower panel, and a liquid crystal layer is interposed between the alignment layers. Application of different voltages to the pixel electrodes and the common electrode generates an electric field, and liquid crystal molecules in the liquid crystal layer are reoriented by adjusting the electric field. The change of the orientations of the liquid crystal molecules in turn changes the transmittance of light passing through the liquid crystal layer, and thus desired images can be obtained by controlling the voltage difference between the pixel electrodes and the common electrode.
The voltages applied to the pixel electrodes and the common electrode are selectively transmitted from a plurality of circuit elements for driving and controlling the voltages, and the voltages applied to the pixel electrodes are switched by the TFTs. The circuit elements include a gate driver supplying gate signals for turning on and turning off the TFTs, a data driver supplying data voltages to be applied to the pixel electrodes, and a timing controller for controlling the gate driver and the data driver and transmitting image data from an external source to the data driver.
A plurality of transmission lines are required for signal transmission in an LCD, and they generate a lot of electromagnetic interference (EMI) the data. Differential transmission such as LVDS (low voltage differential signaling) and RSDS (reduced swing differential signaling) is suggested for reducing the EMI. LVDS is usually used for data transmission for a system to an LCD, and RSDS is generally used for the data transmission from the signal controller to the gate driver and the data driver.
The differential transmission transmits data in pairs of positive and negative signals. Since the data are recognized as the difference between the voltages of the pairs of positive and negative signals, data loss due to noise is reduced. In addition, the electromagnetic waves from the pairs of positive and negative signals are cancelled to reduce EMI.
A conventional technique provides termination resistors for detecting the voltage difference between positive signals and negative signals in pairs at external input terminals of a differential signal amplifying circuit. Since a termination resistor is required for a couple of transmission lines, the number of the termination resistors is determined by the number of the transmission line. For example, 8-bit data transmission using four data channels and one clock channel requires five termination resistors.
Generally, a differential signal amplifying circuit is implemented as a chip mounted on the PCB, while termination resistors therefor are formed on a printed circuit board (PCB) instead of being incorporated into the chip. Accordingly, shapes and positions of the termination resistors depend on sizes and positions of the PCB and the chip and the termination resistors may be spaced apart from the chip. The existence of the termination resistors on the PCB yields complexity in design of the PCB, and long and curved transmission lines for connecting the termination resistors and the chip on the PCB increase EMI.